Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$89.83	11.337%	$100.014	$100.01	$100.00	$100.00
Purchase #2	$240.40	8.153%	$259.9998	$260.00	$260.00	$260.00
Purchase #3	$105.70	5.291%	$111.2926	$111.29	$111.30	$111.30
Purchase #4	$152.42	13.572%	$173.1064	$173.11	$173.10	$173.10
Purchase #5	$242.50	6.223%	$257.5908	$257.59	$257.60	$257.60
Purchase #6	$116.50	6.585%	$124.1715	$124.17	$124.15	$124.20
Purchase #7	$168.89	12.527%	$190.0469	$190.05	$190.05	$190.00
7 purchase totals =	$1,116.24		$1,216.2220	$1,216.22	$1,216.20	$1,216.20